1. Field of the Invention
This invention relates to blade sharpening and more particularly to sharpening curved blades using power driven sharpeners and a mechanism for locating and guiding the blades during sharpening.
2. Prior Art
The present invention is an improvement over the sharpening device shown in U.S. Pat. No. 4,528,778, which provides a blade holder for moving a blade horizontally in a straight line across the face of a sharpening wheel and across a buffing wheel, both driven on a common shaft. The blade holder is supported by three pivoted links located midway between the two wheels. The blade holder can be removed from the supporting link after a blade is sharpened and resecured upside down to facilitate buffing the sharpened blade on the buffing wheel.
Many blades, including scissors blades used in the poultry industry, are curved. That is, the blades curve in a direction transverse to the direction of extent of the blade. Consequently, the blade cutting edge defines an arcuate line lying in a plane perpendicular to the direction of extent of the blade. When such a blade is ground with a single bevel terminating in the cutting edge, as is common with a scissors blade, the plane of the blade is inclined relative to the grinding surface as the blade is moved across the surface. That is, the major plane of the blade is not located in a plane that passes through the center of a grinding wheel. As a result of this orientation, the cutting edge and beveled face present a curved surface (approximating a conic surface section) to the blade-sharpening surface.
If sharpening a curved blade is attempted using the prior art sharpening device, the blade is maintained in contact with the wheel while being drawn across the wheel periphery in a direction parallel to the wheel axis. The blade supporting pivoted links are constrained against motion out of a horizontal plane so that, although the curved blade can be engaged with the wheel and moved horizontally across the wheel periphery, the blade can not be shifted vertically relative to the wheel. Because the blade curves, the locus of engagement between the wheel periphery and the blade will shift about the wheel periphery as the blade moves. Shifting the locus of engagement in this manner will change the bevel angle proceeding along the blade and, at least eventually, produce a cutting edge which no longer lies in the plane perpendicular to the direction of extent of the blade. Consequently, blade performance, particularly in the case of curved scissors blades, may degenerate over time with repeated sharpenings.
The present invention provides a new and improved blade sharpening method and apparatus effective to sharpen curved blades so that the cutting edge remains substantially disposed in a plane perpendicular to the direction of extent of the blade even after numerous sharpenings.